Submitting a Design for Save the Date Originals just to print:

You may be interested in having STDO print your own design on something like a magnet or card. STDO will need to see your design to determine if this is possible.

If you have created something in Word or PowerPaint, or another similar program, the designer will have to recreate your design for printing. Those programs just do not seem to produce print quality files. Often, the designer will need to recreate designs to accommodate the needed resolution, size, margins, and color scheme.
Customers will sometimes try to send images they found on the internet to use- this generally does not work. The size & resolution that most images are on a website is much lower than would be needed for a decent good print. The most common issues that customers run into when they try to submit their own designs are: border size, how close text is to the edge of the product, and, text size.

The designer can provide PDF files at the correct resolution with bleed and safety margins for you to work with.

A few rules of thumb:

1) Do not move text very close to the edge of your design.
2) If you are going to include a border next to the edge of your design, it should be at least 3/16ths of an inch thick. No skinny borders near the edge of the design.
3) No tiny text/wording! Fonts like "Times" can be as small as 12 point. Swirly fonts like "Scriptina" are much thinner, though, and have an even larger minimum size (all the way up to 24pt).
4) File resolution should be 300-600dpi
5) Do not include copyrighted images in your design unless you own the rights (photos, logos, paintings...)
6) Bleed and safety margins are about 1/8th of an inch
Even if you are familiar with graphic design for the internet, you might not know everything about design for print (like bleed and safety margins) so if you can provide a working PSD or AI file for the designer to fiddle with, that works best.
Files can be emailed. Files can be sent via a sharing program like "Drop Box" or Google Documents. If you have an FTP program, a login and password can be set up for you to send your artwork.
Oh, and in case you are wondering, there is no discount for sending in a file to be printed. The pricing tables for magnets and cards that you find around the website is the final pricing.